Method of processing monofilament yarn



4 M. H. COMER ETAL 3,162,995

METHOD OF PROCESSING MONOFILAMENT YARN Filed Sept. 11, 1961 2 Sheets-Sheet 1 INVENTORS! 7 L/ MARVIN H. COMER and CARL. W. THoMAs ATTORNEYS Dec. 29, 1964 M. H. COMER ETAL 3,162,995

METHOD OF PROCESSING MONOFILAMENT YARN Filed Sept. 11, 1961 2 Sheets-Sheet 2 INVENTORSI MARV H. CoM E12 and CARL. THoMAs BY 26km, W

ATTORNEYS United States Patent METHOD GE PROCiiSSfiQG MQNGFILAMENT Marvin H. {joiner and (Jeri W. Thomas, both of Burlington, NC, assignors, by mesne assignments, to Bearing Millikan Research Corporation, Spartanhurg, S.C., a

corporation of South Carolina Filed Sept. 11, 361, Ser. No. 137,382 9 Claims. or. 57-15? This invention relates generally to a method of processing monofilament thermoplastic yarn to produce a stretchable yarn having balanced torque and more particularly to a method of producing a stretchable monofilament yarn, such as nylon, which is characterized by a series of small closely spaced substantially uniform springlike helical coils and in which the rotational direction of the coils reverses periodically to thereby balance the torque in the yarn and make it particularly adaptable for the single-feed knitting of stretchable articles of clothing, such as ladies sheer hosiery and the like.

There are many known methods of processing a normally non-stretchable thermoplastic yarn, such as nylon, to produce a yarn which is stretchable or a yarn which forms stretchable fabric when knit. For example, monofilament nylon yarns have been hi hly twisted, heat-set and untwisted to produce a lively or torque yarn which causes the knit stitches of the fabric to distort and produce elasticity in the fabric. Monofilament thermoplastic yarns also have been crimped by means of gears, crimping wheels or the use of a stuffing box. Curl or crimp has also been impar ed to yarn by drawing it over a heated sharpened blade, or around heated cylindrical objects. It is also known to twist yarns together and heat-set them in the twisted-together condition to form helical curls or coils therein.

While the above methods are capable of producing lively, crinkled, curly or coiled yarns which may be knit to form fabric having elastic characteristics, there are various disadvantages and problems with known yarn and methods. For example, the heat-set and twisted yarn as well as that drawn around a cylindrical object has torque or liveliness which must be balanced and controlled. The gear crirnped yarn is distorted in only one plane and lacks desirable bulk. Yarns crimped in a stuffing box lack uniformity of crimp size and uniform setting.

While edge crirnped yarn has balanced torque, uniformity of coil size is difficult to maintain because of variations in the tension of the yarn and the blade cannot be maintained at a constant degree of sharpness. Also, in this process, portions of the yarn which engage the blade are subjected to more heat, and consequently the yarn is not uniformly heat-set throughout its diameter and the curls or coils can be removed if the yarn is placed under very high tension which is close to the breaking point of the yarn. Additionally, the drawin of the yarn over the sharpened blade must be continuous and, if stopped for any reason, such as yarn breakage, the processed yarn must be doifed and cannot be knotted and continued after yarn breakage. Hosiery knit of this type yarn requires excessive agitation in the finishing in order to fully develop the curls or coils.

It has also been proposed that thermoplastic yarns be subjected to first and second false twisting operations to produce a torque-free or balanced torque stretchable yarn which may be utilized to knit fabric in a single-feed manner. These two false twisting operations are superimposed in opposite directions to balance the torsional stress in the yarn and produce a yarn which has a generally wavy appearance. However, this procedure has not been utilized to produce a helical, spring-like yarn having closely spaced coils and balanced torque.

With the foregoing in mind, it is a primary object of the present invention to provide a method of producing all) 3,162,995 Patented Dec. 2%, 1954 an improved stretchable monofilament thermoplastic yarn which has balanced torque and which is suitable for singlefeed knitting of ladies sheer hosiery and the like wherein the torque of the finished hosiery is completely balanced. The yarn produced in accordance with the present method is characterized by a series of helical, spring-like coils of highly convoluted configuration which are of substantially uniform size and configuration. The coils are closely spaced, for example, in 15 denier yarn there are on the order of loops per inch when the yarn is relaxed and approximately loops per inch when placed in 212 F. Water. Yarn produced in accordance with the invention is not subject to the disadvantages of the prior art yarns produced by the above-noted methods.

It is another object of the present invention 'to provide a novel method of producing a yarn of the type described which may be easily knit into ladies sheer hosiery and the like without requiring any changes or special procedures during the knitting and finishing of the hosiery knit therefrom. The uniform loops or coils of the yarn provide uniform stretch in the hosiery and give a bulky appearance with the relaxed and finished fabric having a somewhat pebbled or creped appearance.

It is still another object of the present invention to provide a novel method of producing a yarn of the type described in which the spring-like coils of the yarn are permanently set in the yarn and although these coils can be removed or straightened out by applying tension to the yarn, the coils will return to substantially their original relaxed condition after tension is released from the yarns, even when tension is applied which approaches the breaking point of the yarn.

It is another object of the present invention to provide a novel method of producing a yarn of the type described which can be economically carried out to produce the yarn at a rapid production rate to thereby lower the cost of the yarn.

The foregoing objects as well as other objects are generally accomplished by false twisting a single pair of monofilament thermoplastic yarns in a first direction at a relatively high number of turns, within the range of from 85 to 126 turns per inch, while subjecting the same to a relatively high temperature, then false twisting the same pair of yarns in an opposite direction while reducing the number of turns by approximately one-third and the amount of heat by substantially one-fifth during the second false twisting operation, then separating the yarns and Winding the separated yarns onto separate take-up bobbins.

Some of the objects of the invention having been stated and a general description of the invention having been given, other objects will appear as the description proceeds and as the details of the invention are more fully explored in connection with the accompanying drawings, in which- FIGURE 1 is a somewhat schematic isometric view of the preferred type of apparatus for carrying out the first false twisting operation of the present invention;

FIGURE 2 is a greatly enlarged fragmentary View of the pair of strands of monofilament yarns after the first false twisting operation, the yarns being in partially relaxed position and each strand having a strong tendency to kink and curl upon itself, due to the torsional stress therein;

FIGURE 3 is a somewhat schematic isometric view of the preferred type of apparatus for carrying out the second false twisting operation and illustrating the manner in which the two separate monofilament strands are separated and then taken up on separate take-up bobbins;

FIGURE 4 is a greatly enlarged fragmentary view greases of one of the yarns in relaxed condition after it has been false twisted in the second operation;

FIGURE is a somewhat schematic isometric view of the preferred type of winding machine which is utilized to transfer the processed yarn of the present invention from the take-up bobbins to suitable bobbins for knitting;

FIGURE 6 is a View of the yarn shown in FIGURE 4 after the same has been immersed in boiling water for three minutes and illustrating the manner in which the size of the loops or coils is decreased and the number of coils per inch is also increased;

FIGURE 7 is a greatly enlarged transverse vertical sectional view through the monofilament thermoplastic yarn before it is processed, being taken along the line 77 in FIGURE 1;

FIGURE 8 is a greatly enlarged transverse sectional view through the yarn after it has been processed in accordance with the present invention, illustrating the flattened condition of the yarn;

FIGURE 9 is a. greatly enlarged elevation of the upper end of the false twist spindle used in processing the yarn;

FIGURE 10 is a vertical sectional view taken through the center of that portion of the false twist spindle shown in FIGURE 9;

FIGURE 11 is a greatly enlarged fragmentary portion of the knit fabric illustrating the distortion of the stitch loops before the knit fabric is finished;

FIGURE 12 is a view similar to FIGURE 11 but illustrating the distortion of the stitch loops after the knit fabric is finished.

Generally, the present invention is particularly concerned with a method of processing those monofilament thermoplastic yarns which fall within the range of from about 10 denier to 30 denier and which are most commonly utilized to knit ladies sheer hosiery and the like. Also, in the first false twisting operation, the number of turns imparted is within the range of from 85 to 126 turns per inch in one direction, and in the second false twisting operation, the number of turns is within the range of from 57 to 84 turns per inch in the opposite direction. The false twisted yarns are subiected to a temperature within the range of from 415 F. to 425 F. in the first false twisting operation while the yarns are subjected to a temperature of from 340 F. to 360 F. in the second false twisting operation.

After the pair of monofilament yarns have been processed through the first and second false twisting operations and separated, they each have a series of convolutions or coils which are spring-like in appearance and the coils or loops are of uniform size with an adajcent group of the loops being formed in one direction and the next group of loops being formed in an opposite direction, the number of loops in each group varying before a reversal point is reached. After the yarns have been processed through the first false twisting operation, each filament is very lively and contains a great deal of torque and will kink and twist upon itself when relaxed, however, after the yarn is processed through the second false twist operation, the torque is balanced and contains uniform loops which periodically reverse their direction along the length of the yarn. When this yarn is placed under longitudinal tension, close to the breaking point, the loops will straighten out, however, when the tension is released, they will return and the loops or coils are not materially effected but return to substantially their original configuration. When the yarn is relaxed, it will not kink and curl upon itself because the torque is balanced. Immediately after processing, the relaxed yarn is elastic and stretchable and the loops are closely spaced-about an average of 75 coils per inch for 15 denier. It has been found that after this yarn is knit into a fabric, such as ladies sheer hosiery and then finished in the usual manner, even a greater amount of elasticity is developed. This has been demonstrated by subjecting an untensioned skein of the yarn to boiling water for a period of three minutes. After this water treatment and relaxing operation, it has been foun that the coils are reduced in size so th at there is an average of coils per inch for 15 denier yarn.

During the knitting operation, the yarn is maintained straight and after the knit loops are shed from the needles, the stitch loops are somewhat distorted in an irregular manner as the yarn attempts to return to the original coiled position. After the knit fabric is finished, the stitch loops are very distorted and some of the stitch loops will distort toward one face of the fabric, others will distort or bow or bend toward the opposite face of the fabric, while other stitch loops will distort in opposite directions parallel to the suraces of the fabric so that the relaxed fabric has a somewhat pebbled or creped bulky appearance. However, when the fabric is stretched, as when a hose is worn on the leg, the distorted stitch loops and the yarns forming the same will substantially straighten and the stitches will assun e their normal shape, thereby presenting a sheer appearance when worn on the leg.

There are several known types of thermoplastic yarns which are commercially available and which may be rendered stretchable according to the present method and while the present application is particularly concerned with nylon, other yarns having similar characteristics may be utilized. Yarns, such as nylon, are substantially round or circular in cross-section before processing and it has been found tr at the processing of these yarns in accordance with the present method causes the same to become flattened or somewhat rectangular in cross-section. It is believed that the yarns are flattened because they are initially twisted together to a relatively high degree and heated close to the melting point so that they flatten against each other. Also, the yarn is contracted about 14% due to the high twist, and has about shrinkage during this process.

Referring of the drawings, FIGURE 1 schematically illustrates the apparatus used to false twist the yarns in the first operation. The drawing shows only one section of a slightly modified conventional false twist machine of the type which is known as the Model 551 Superloft machine manufactured by Leesona Corporation. A pair of monofilament thermoplastic yarns Y and Y are withdrawn from respective yarn supply pirns and 21 which are suitably supported on the lower portion of the machine. The yarns Y and Y are in the condition received from the yarn producer and are withdrawn directly from the pirns 2d and 21 on which the yarn is wound by the producer. As shown in FIGURE 7, the yarns are round in cross-section as they are drawn from the pirns 2d and Zl, before processing.

The pair of yarns Y and Y pass upwardly through a common guide eye 22 where they are joined together and guided through a pair of tension disks 23. The yarns then pass beneath a yarn guiding element 24 and then are wound around a driven feed roll 25. From the feed roll 25, the yarns Y and Y extend upwardly pass through a yarn receiving groove 26 in a heater block 27, From the heater block 27, the yarns Y and Y pass over a yarn guide element 3% and into a false twist spindle 3i which is rotated by a belt 32.

As shown in FIGURES 9 and 10, the upper end of the false twist spindle 31 is provided with a small exit pin 33 which is tapered inwardly toward the center from each end and which is formed of a hard ceramic material, such as alsimag. The center diameter of the pin 33 is small, on the order of .030 of an inch. As the yarns leave the exit pin 33 of the false twist spindle 31, they are passed through a guide eye 34 and through a guide block 35 which is suitably supported on a traversing rod 36. From the guide block 35, the yarns are wound onto a take-up bobbin or spool 37 which is driven by a roller 38.

During this first false twisting operation, the machine is set up to drive the false twist spindle 31 at a speed of 147,000 revolutions per minute by the belt 32. The speed of the feed roll 25 and the take up roll 38 is adjusted to impart between 85 and 126 turns per inch of false twist to the yarns in one direction. The temperature of the heater block 27 is maintained between 415 F. and 425 F. and the tension disks 23 are adjusted to apply substantially 3 to 4 grams of tension on the yarns Y and Y after they are drawn from the supply pirns. From 6 /2 to 7 grams of tension is maintained in the yarns as they pass through the heater block 27 and approximately 8 to 14 grams of tension is maintained in the yarns as they are wound onto the take-up spool 37. Also, the speed of the feed roll 25 and the take-up roll 38 are adjusted to apply from overfeed to approximately 6.2% overfeed. The exact number of turns of false twist imparted, the temperature of the heater and the amount of overfeed have been determined for yarns of different deniers and these are set forth later.

A close inspection of the yarns Y and Y, following the first false twist operation (FIGURE 2), reveals that they have become somewhat flattened or ribbon-like ('FiG URE 8) and each yarn contains a great deal of torsional stress so that it tends to curl and kink upon itself when partially relaxed, as shown in FIGURE 2. If the pair of strands Y and Y were completely relaxed in FIGURE 2, they would completely twist together since each of the yarns is very lively. The yarns shown in FTGURE 2 are somewhat kinked because they are in partially relaxed condition, however, when these yarns are wound onto the take-up spool 37, with from to 14 grams of tension, they are maintained in substantially a straight condition.

In the second false twisting operation, the take-up spool 37 is used as the supply spool on a second Model 551 Superloft machine which has been slightly modified to again false twist the yarns. As shown in FIGURE 3, the spool bobbin 37 is rotated by a drive roll 4! as the yarns Y and Y are withdrawn therefrom and guided over a bar 41 which has been attached to and spaced above the usual traversing bar 42 of the machine. The yarns are guided downwardly from the bar 41 and pass beneath a grooved guide pulley 43 which is supported on the forward end of a support arm 44. The yarns are guided from the pulley 43, beneath a yarn guide element 45 and wrapped around a feed roll 4d. From the feed roll 46, the yarns are passed upwardly through a yarn receiving groove 47 in a heater block 50. From the heater block St), the yarns pass upwardly beneath a yarn guide element 51 and through a false twist spindle 52 which is rotated by a driving belt 53.

As the yarns leave the false twist spindle 52, they are separated, as at 54, and engage spaced apart grooved guide pulleys 55 and 56 which are supported on and beneath a conventional traversing bar 6t). From the pulleys 55 and 56, the yarns Y and Y pass through guide blocks 61 and 62 supported on the traversing bar at and they are then wound onto separate respective take-up bobbins or spools 64 and 65 which are rotated by respective driving rolls 66 and 67.

In this second false twisting operation, the machine is set up to drive the false twist spindle 52 at a speed of 90,000 revolutions per minute by the belt 53. The speed of the rolls 40, 4-6, 60 and 67 is adjusted to impart between 57 and 84 turns per inch of false twist to the yarns in a direction opposite the twist imparted in the first false twisting operation while providing from 0% to 6.2% overfeed. Also, the heater block temperature is maintained between 340 F. and 360 F. during this second false twisting operation. The machine is set up to pro vide 3 to 4 grams of tension in the yarn from the supply spool 37 to the feed roll 46, from 2 to 3 grams at the heater block 50, from 12 to 14 grams above the false twist spindle 52 and from 10 to 12 grams as the yarns are wound onto the separate take-up spools 64 and 65. As the yarns pass through the second false twisting spindle 6 52, they are again passed around an exit pin which is similar to the exit pin 33, shown in connection with the false twisting spindle 31 used in the first false twisting operation.

Referring to FIGURE 4, the yarn strand Y is shown after it is removed from the take-up spool 64 and allowed to relax. It will be noted that the coils are substantially uniform in size and the coils adjacent opposite ends of the yarn shown in FiGURE 4 rotate in one direction and then reverse their directions, at the points indicated at 70, and the coils in the medial portion of the yarn shown in FIGURE 4 rotate in the opposite direction. This reversal of the direction of rotation of the coils in the yarn occurs periodically throughout the length of the yarn and the overall torque of resulting yarn is balanced so that it can be knit single-feed to form ladies sheer hosiery and the like.

After the yarns are wound onto the spools 64, 65, they are placed on a suitable winding machine, such as a Speedex machine of the type manufactured by Fletcher Works of Cheltenham, Pennsylvania. The spool 64 is shown in position at the lower end of the winding apparatus (FIGURE 5) and is provided with aluminum guide cap 72 which is positioned to cover the upper end of the spool 64. The yarn Y is drawn upwardly from the spool 64 and passes through a guide eye73, over a guide rod 74, over a revolving applicator 75 which is running in a trough 76 filled with a lightweight oil which adds to the evenness of the curls, the oil being of a type that allows the yarn to relax more readily to its position to the originally set curls.

The yarn Y passes from the roll 75 through a guide wire member 77 and upwardly through a guide block 73 which is supported on a traversing bar- 79. The yarn then passes through the slot of a slub catcher blade 8i) which is supported on the bar 79 behind the guide block 78. The yarn Y is then wound onto a suitable tube 81 which is then used as a supply bobbin on the knitting machine.

The Winding operation shown in FIGUREJ is carried out to lubricate the yarn and to place it on a supply tube by what is known as a filling wind so that it may be easily withdrawn during knitting on a circular knitting machine.

As heretofore stated, the present invention is particularly concerned with a method of processing monofilament thermoplastic yarns which range from 10 to 30 denier and are suitable for knitting sheer fabrics, such as ladies sheer hosiery and the like. The number of turns imparted in each of the false twisting operations, the temperature and the amount of overfeed is important, and it has been found that these factors must be carefully controlled to produce a satisfactory yarn. Specific examples which produce satisfactory yarns are set forth in the following charts:

First False Twist Operation 10 12 15 20 30 denier denier denier denier denier Amount of False Twist,

t.p.i.-Z 126 106 106 95 Heater Block Temperature,

F 415 415 415 420 425 Overioed, percent" 6. 2 0 0 0 0 Second False Twist Operation 12 15 20 230 denier denier denier denier denier Amount of False Twist,

t.p.i.-S 8d 71 71 -63 57 Heater Block Temperature,

F 355 340 340 350 360 Overfeed, percent 6.2 v0 0 0 0 It is immaterial which direction the false twist is imescapes parted in the first operation, as long as the false twist imparted in the second operation is in a reverse or opposite direction.

In order to illustrate the manner in which the elasticity of the yarns and fabric knit therefrom is fully developed when the fabrics are subjected to the usual finishing operations, relaxed skeins of the processed yarns have been immersed or dipped in boiling, 212 F., water for three minutes. The yarn shown in FIGURE 6 represents the appearance of the yarn of the present invention when its elasticity has been fully developed in hot water. As shown in FIGURE 6, the loops or coils are closer together than the coils of the yarn shown in FIGURE 4 and the coils of the yarn of FEGURE 6 are smaller than the coils of the yarn of FIGURE 4. It has been determined that 15 denier yarn, after the second false twisting operation, has an average of '75 coils per inch (FIGURE 4) and that after the elasticity of the yarn has been fully developed (FIGURE 6), there are 85 coils per inch, on the average.

The fragmentary portion of fabric shown in FZGURE 11 is greatly enlarged and illustrates the appearance of the stitch loops immediately after the fabric is knit from the yarn formed in accordance with the method of the present invention and it will be noted that there is only a slight distortion of the lrnit stitch loops. Also, this view clearly brings out the flat nature of the yarns.

Referring to FlGURE 12, it will be noted that the stitch loops of the fabric are greatly distorted and the fabric has greater bulk and extensive stretchability. The fabric shown in FIGURE 12 has been subjected to the usual finishing operation which includes preboarding, dyeing, scouring and then final-preboarding and the full elasticity or distortion of the stitch loops is developed without excessive agitation of the fabric.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

We claim:

1. A method of processing a monofilament thermoplastic yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance th overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawing together first and second only monofilament yarns from separate yarn supply sources,

(b) joining the separate yarns together,

(0) false twisting the joined together yarns with about 85 to 126 turns of false twist in one direction while heat-setting the yarns,

(d) subsequently false twisting the yarns a second time in the opposite direction while reducing the number of turns imparted by substantially one-third of the number of turns imparted in the first false twisting step and while heating the yarns in the second false twisting operation at a temperature lower than in the first false twisting operation,

(e) separating the two yarns, and

(f) taking up the separated yarns on separate bobbins.

2. In a method according to claim 1 wherein the monofilament yarns processed are within the range of from 10 to 30 denier.

3. In a method according to claim 1 wherein the number of turns of false twist imparted in the step (d) is within the range of from 57 to 84 turns per inch.

4. In a method according to claim 1 wherein the yarns are false twisted in steps (0) and (d) by passing the same through a false twist zone and thence through a twist stop zone wherein the yarn is caused to describe a path having 360 degree turn to provide a yarn coil diameter of about 0.030 of an inch.

5. A method of processing a mon'ofilament thermoplastic yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance the overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawi together first and second only 10 denier monofilament yarns from separate yarn supply sources,

(b) joining the separate yarns together,

(c) false twisting the joined together yarns with about 126 turns of false twist per inch in one direction while heat-setting the yarns by passing the same through a heating zone maintained at a temperature of about 415 F,

(c) subsequently false twisting the yarns a second time with about 84 turns of false twist per inch in the opposite direction while passing the same through a heating zone maintained at a temperature of about 355 F,

(e) separating the two yarns, and

(f) taking up the separated yarns on separate bobbins.

6. A method of processing a monofilament thermoplastic yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance the overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawing together first and second only 12 denier monofilament yarns from separate yarn supply sources,

(5) joining the separate yarns together,

(0) false twisting the joined together yarns with about 106 turns of false twist per inch in one direction while heat-setting the yarns by passing the same through a heating zone maintained at a temperature of about 415 F.,

(d) subsequently false twisting the yarns a second time with about 71 turns of false twist per inch in the opposite direction while passing the same through a heating zone maintained at a temperature of about 340 F,

(e) separating the two yarns, and

(f) taking up the separated yarns on separate bobbins.

7. A method of processing a monoiilament thermoplastic yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance the overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawing together first and second only 15 denier m'onofilament yarns from separate yarn supply sources,

(5) joining the separate yarns together,

(0) false twisting the joined together yarns with about 106 turns of false twist per inch in one direction while heat-setting the yarns by passing the same through a heating zone maintained at a temperature of about 415 F.,

(d) subsequently false twisting the yarns a second time with about 71 turns of false twist per inch in the opposite direction while passing the same through a eating zone maintained at a temperature of about 340 1 (e) separating the two yarns, and

(f) taking up the separated yarns on separate bobbins.

8. A method of processing a monofilament thermoplastie yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance the overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawing together first and second only 20 denier monofilament yarns from separate yarn supply sources,

([2) joining the separate yarns together,

(0) false twisting the joined together yarns with about 95 turns of false twist per inch in one direction while heat-setting the yarns by passing the same through a heating zone maintained at a temperature of about 420 F.,

(d) subsequently false twisting the yarns a second time with about 63 turns of false twist per inch in the opposite direction while passing the same through a heating zone maintained at a temperature of about 350 F.,

(e) separating the two yarns, and

(f) taking up the separated yarns on separate bobbins.

9. A method of processing a monofilament thermoplastic yarn to produce a plurality of small closely spaced, substantially uniform, spring-like helical coils therein, the rotational direction of said coils periodically reversing along the length of the yarn to balance the overall torque of the yarn and provide a stretchable yarn suitable for single-feed knitting of hosiery and the like, said method comprising the steps of:

(a) drawing together first and second only 30 denier monofilament yarns from separate yarn supply sources,

(b) joining the separate yarns together,

(c) false twisting the joined together yarns with about 85 turns of false twist per inch in one direction while heat-setting the yarns by passing the same through a heating zone maintained at a temperature of about 425 F.,

(d) subsequently false twisting the yarns a second time with about 57 turns of false twist per inch in the opposite direction while passing the same through a heating zone maintained at a temperature 'of about 360 F.

(e) separating the two yarns, and

(7) taking up the separated yarns on separate bobbins.

References Cited in the file of this patent UNITED STATES PATENTS 2,777,276 Klein Jan. 15, 1957 2,881,504 Billion Apr. 14,1959

FOREIGN PATENTS 788,944 Great Britain Jan. 8, 1958 

1. A METHOD OF PROCESSING A MONOFILAMENT THERMOPLASTIC YARN TO PRODUCE A PLURALITY OF SMALL CLOSELY SPACED, SUBSTANTIALLY UNIFORM, SPRING-LIKE HELICAL COILS THEREIN, THE ROTATIONAL DIRECTION OF SAID COILS PERIODICALLY REVERSING ALONG THE LENGTH OF THE YARN TO BALANCE THE OVERALL TORQUE OF THE YARN AND PROVIDE A STRETCHABLE YARN SUITABLE FOR SINGLE-FEED KNITTING OF HOSIERY AND THE LIKE, SAID METHOD COMPRISING THE STEPS OF: (A) DRAWING TOGETHER FIRST AND SECOND ONLY MONOFILAMENT YARNS FROM SEPARATE YARN SUPPLY SOURCES, (B) JOINING THE SEPARATE YARNS TOGETHER, (C) FALSE TWISTING THE JOINED TOGETHER YARNS WITH ABOUT 85 TO 126 TURNS OF FALSE TWIST IN ONE DIRECTION WHILE HEAT-SETTING THE YARNS, (D) SUBSEQUENTLY FALSE TWISTING THE YARNS A SECOND TIME IN THE OPPOSITE DIRECTION WHILE REDUCING THE NUMBER OF TURNS IMPARTED BY SUBSTANTIALLY ONE-THIRD OF THE NUMBER OF TURNS IMPARTED IN THE FIRST FALSE TWISTING STEP AND WHILE HEATING THE YARNS IN THE SECOND FALSE TWISTING OPERATION AT A TEMPERATURE LOWER THAN IN THE FIRST FALSE TWISTING OPERATION, (E) SEPARATING THE TWO YARNS, AND (F) TAKING UP THE SEPARATED YARNS ON SEPARATE BOBBINS. 